The present invention relates to hard disk systems, and in particular to a micrometric actuation, hard disk read/write unit.
As known, hard disks are the most commonly used means of storing data in personal computers. Consequently they are produced in very large volumes, and the maximum data storage density is increasing year by year. Hard disks are read and written by actuator devices, the general structure whereof is shown in FIGS. 1 and 2 and is described hereinafter.
In particular, FIG. 1 shows a known actuator device 1 of a rotary type, comprising a motor 2 (also called a voice coil motor), secured to a support body 3, generally called E-block, owing to its shape as an xe2x80x9cExe2x80x9d in lateral view (see, e.g., FIG. 2). The support body 3 has a plurality of arms 4, each of which supports a suspension 5, formed from a steel plate, and secured in a projecting manner. At an end not secured to the support body 3, each suspension 5 supports a coupling 8 (called a gimbal or a flexure), also made of steel, which in turn supports a read/write transducer 6 (called a slider), which (in the operative condition) faces a surface of a hard disk 7.
The slider 6 comprises a support body, a bearing secured thereto, and a magneto/resistive and inductive read/write (R/W) head 91 that forms the actual reading and writing device. Electric wires (not shown) extend from the R/W head 91, along a coupling 8 and the suspension 5, as far as a signal processing device (also not shown), secured to a main board of a personal computer or other device that contains hard disks for data storage.
To prevent the read/write signal from becoming excessively attenuated, to ensure that it has sufficient amplitude for reading/writing of the hard disk 7, and also to prevent the hard disk 7 from being damaged by the slider 6, the slider 6 must be maintained at a predetermined distance (which at present is 20-30 nm) from, and parallel to, the hard disk 7. Consequently, the suspension 5 has a degree of freedom in a vertical direction, to regulate the distance of the slider 6 from the hard disk 7. The coupling 8 has two degrees of freedom around two axes xcfx86 and "psgr" in a horizontal plane, and can carry out pitch and roll movements, to maintain the slider 6 parallel to the hard disk 7 even in presence of roughness and non-planar points. In particular, the suspension 5 should support the weight of the slider 6 (now 1.5 mg), and should also be able to oppose pressure generated on the surface of the slider 6 by air interposed between the hard disk 7 and the slider 6 and biasing the slider 6 away from the disk 7 during movement of the hard disk 7 and/or the actuator device 1.
For this purpose, after assembling the various components, the suspension 5 is permanently bent, exploiting plastic deformation characteristics of steel. If the suspension is bent too much or too little, the bending error cannot be corrected, and it is necessary to scrap the suspension 5 and the elements secured to it (e.g., the flexure 8 and the slider 6). Now, the assembly process, including the above-described bending step, has an output efficiency of 65-75%, giving rise to high costs for scrap. Furthermore, in some cases, the bending error is detected only upon completion of installation on the hard disk 7, thus further aggravating the problem of costs.
In currently commercially available hard disk read/write devices, the slider 6 is glued directly to the coupling 8. To obtain more accurate and finer control of the position of the slider 6, it has already been proposed to use a double actuation step, with a first, courser actuation stage, including the motor 2, displacing the assembly formed by support body 3, suspension 5, flexure 8 and slider 6, across the hard disk 7, during the approximate track search, and a second actuation stage, effecting a finer control of the position of the slider 6, during tracking.
Hitherto, two solutions have been proposed. According to a first solution, the suspension 5 or the support body 3 is modified, such as to control in a micrometric manner the position of the suspension 5. According to a second solution, the position of the slider 6 with respect to the end of the suspension 5 is controlled through a microactuator, interposed between the slider 6 and the coupling 8.
An example of an embodiment of a microactuator 9 of a rotary electrostatic type, usable for the second micrometric actuation solution, is represented schematically in FIG. 3, wherein only part of the microactuator 9 is completely shown, owing to the axial symmetry. The microactuator 9 comprises a stator 17, integral with a dice integrating the microactuator 9 and glued to the coupling 8, and a rotor 11, capacitively connected to the stator 17, to be glued to the slider 6 (see, e.g., FIG. 2).
The rotor 11 comprises a suspended mass 12, of a substantially circular shape, and a plurality of mobile arms 13, extending radially towards the exterior from the suspended mass 12. Each mobile arm 13 supports a plurality of mobile electrodes 14, extending in a substantially circumferential direction and equidistant from one another. The rotor 11 also comprises resilient suspension and anchorage elements (spring 15), to support and bias the rotor 11 via fixed regions 16.
The stator 17 comprises a plurality of fixed arms 18, 19, extending radially and supporting each a plurality of fixed electrodes 20. In particular, each mobile arm 13 is associated to a pair of fixed arms, formed by a fixed arm 18 and a fixed arm 19. The fixed electrodes 20 of each pair of fixed arms 18, 19 extend towards the associated mobile arm 13, and are intercalated or interdigitated with the mobile electrodes 14. The fixed arms 18 are all arranged on a single side of the respective mobile arms 13 (on the right, in the example of FIG. 3), and are all biased to the same potential, via biasing regions 21. Similarly, the fixed arms 19 are all arranged on the other side of the respective mobile arms 13 (on the left, in the example of FIG. 3), and are all biased to the same potential via biasing regions 22.
The fixed arms 18 and 19 are biased to different potentials, so as to generate two different potential differences with respect to the mobile arms 13, and to cause rotation of the rotor 11 in one direction or the other.
However, the insertion of the microactuator 9 between the coupling 8 and the slider 6 causes a reduction in the assembly output of the read/write device, because of the criticalities of the microactuator 9.
An embodiment of the invention provides a read/write unit not affected by the above-described disadvantages.
According to embodiments of the present invention, a read/write unit for hard disks and a manufacturing method are provided, as defined in the claims.